1. Field of the Invention
This disclosure relates to the field of cyclonic separators and the use of cyclonic flows to separate and isolate particles. In particular, this disclosure relates to the designs of cyclonic separator systems that allow particles in a particular size band to be collected and transferred to a separate flow as well as designs that lead to the reduction of particle buildup in the cyclonic flow generator and related components.
2. Background of the Invention
The cyclonic separator is a well known general technology having applications from scientific research to today's bagless vacuum cleaners. The principle of operation is theoretically quite simple; the cyclonic separator uses rotational motion, and changes in rotational motion velocity to precipitate particles out of an air flow. In the case of a vacuum cleaner, the cyclonic motion deposits particles of a particular size or larger into a collection bin, then returns the air flow to the outside. In this way the dust and particles captured by the vacuum cleaner can be collected and disposed of.
Since the use of anthrax in the United States mail in October 2001, government organizations have become increasingly interested in detecting dangerous substances such as microorganisms, chemicals, or biological warfare agents which could be unleashed on the United States to promote the agenda of a terrorist organization.
The transmission of agents is particularly of concern when used in aerosolized form where early detection may be difficult. Because large buildings, subway systems, and the like utilize air circulation systems in relatively self contained environments there is increasing concern that the ventilation systems of these environments could be used in an attack to spread a dangerous warfare agent quickly and in a manner that is difficult to detect. This scenario raises the level of interest in aerosolized contaminant detection.
The detection of aerosolized contaminants also commands great interest because it provides for a relatively easy and unobtrusive way to monitor objects which might contain a warfare agent. No matter how careful a person is, generally some particles of an agent are released into the atmosphere when that agent is being packed, transported, or loaded in preparation of its being unleashed. The inability to completely contain the agent has led to a plethora of searching devices to detect warfare agents as well as other potentially aerosolized substances released from the surface of an item. Bomb- or illegal drug-sniffing dogs searching for such residue on luggage or packages are one such technology of this type where the dog's nose can detect a minute amount of particles aerosolized by the object's passing.
Another way to obtain samples of particulates that may be present in or on an object, is to use air to directly aerosolize the residue and carry it to a detector. Air may be purposefully flowed over objects of interest to dislodge and collect the minute particles without risk of damage or loss of privacy. U.S. patent application Ser. No. 10/449,612, the entire disclosure of which is herein incorporated by reference, describes embodiments of a system for obtaining aerosolized samples of materials on or potentially included in mail.
One of the leading problems with aerosolized samples produced by these methods and even those produced through other actions, however, is that there is a large amount of air involved, even in a small application, and that air naturally includes a huge number of particles which are not of interest. Pollens, dust, pollutants, atmospheric microorganisms and other materials are always in the air to be sampled, thus making detection of the particles of interest more challenging.
Further, detectors sensitive to particular biological or chemical items of interest, generally have to process every particle they are provided with. As the air will naturally include many particles which are not of interest, it is desirable to separate out as many of those particles as possible before providing the air to the detector while still allowing particles potentially of interest to be provided to the detector. Uninteresting particles can clog the detector over time, increasing the amount of maintenance required or decreasing the detector's life. It is therefore desirable to remove them from the air stream provided to the detector.
Still further, to detect a multitude of chemical or biological materials, it may be necessary to have multiple different types of detectors. Each detector must process every particle in the air stream provided to it to determine its relevance. Where each detector is provided the air flow sequentially, detection may be too slow and cumbersome, especially where large air flow volumes need to be monitored. Further, depending on the type of detector, if too many uninteresting particles are present, detection of particles of interest could become too attenuated.
Because of problems such as the above, most chemical and biological systems utilize some form of particle separator to eliminate particles which are known to not be particles of interest. For example, if a particular microorganism is being sought to be detected, particles which are dramatically smaller or dramatically bigger than the microorganism do not need to be tested. Traditionally, the particles have been separated using filters or cyclonic separators. Both these systems have a very noticeable problem, however, in that they cannot provide particles in a size range that does not include one of the small or large size extremes. A cyclonic separator will trap all particles of the desired size and larger, whereas a filter can only allow passage of particles of the desired size and smaller, trapping those particles of a larger size. These methods also have the problem that they require regular checking to prevent clogging. In sum, this generally means that particles either above or below a particular size may be analyzed, but there is no reasonable way to get particles in a particular range or band.
These methods also have trouble in applications where there are a substantial number of particles present which are either larger or smaller than the particles of interest and which cannot be well separated by the chosen methodology. In particular, if the desired particle is quite small and the system is operating in a dusty environment where there are a large number of uninteresting particles of relatively large size, a cyclonic separator will generally provide too many particles to a detector, while a filter will rapidly become clogged and fail.
Beyond the problems of inefficient separation, there is also the problem that filter media and cyclonic separators will often stop particles of interest through deposition, either on the filter media (particularly if it is getting clogged) or on the surface of the cyclonic separator or related structures during the cyclonic separation. Such trapping of particles of interest means that trace amounts which may need to be detected, are instead confined to the separator and its related structures.